Jump to content

C Model Fuel Burn Rate


Recommended Posts

8 hours ago, cliffy said:

 

If you lean below the wide open throttle enrichment point, that point has no meaning (or that throttle position). All the leaning is done downstream of that FF position. I.E., if you see it go from 14 to 12.5 as you move the throttle plate and then you lean with the mixture to 10 GPH the throttle position at 12.5 has no meaning (except maybe to even out distribution).

I've read from multiple different sources the intake system on these engines were designed for a flat plate at WOT for maximum efficiency. Of course I don't have a DEM so I don't know how my spread is, etc. But the enrichment circuit is a good point- its all taken care of by the red knob anyways

Link to comment
Share on other sites

2 hours ago, Raptor05121 said:

I've read from multiple different sources the intake system on these engines were designed for a flat plate at WOT for maximum efficiency. Of course I don't have a DEM so I don't know how my spread is, etc. But the enrichment circuit is a good point- its all taken care of by the red knob anyways

Our carbs do not put out even mixtures to each cylinder. Reducing throttle angles the plate inside with the goal of creating turbulent flow, which will better atomjze the fuel and more thoroughly mix it into the air flow. This doesn't apply to the injected engines, they have no carb so their procedures are different . . . .

  • Like 1
Link to comment
Share on other sites

it doesnt exist. but it has been observed by carbureted engine owners that a slightly cocked throttle will even out the mixture distribution. One RV8 guy i personally know, ran his O-360 LOP for 1000 hours this way.

Link to comment
Share on other sites

9 minutes ago, cliffy said:

Can anyone provide any official info from the manufacturer that pulling back the throttle produces better fuel distribution vs WOT?

We don't need info from the manufacturer...  We have numerous people with engine monitors who can show that the egts and chts even out with a little pull back from full throttle.  I would be careful doing it too much if you don't have such a monitor, but it is a tried and true practice.  It has shown itself especially helpful on the 6 cylinders.  It has noticeable benefits  on our 4 cylinders as well.

Link to comment
Share on other sites

10 minutes ago, cliffy said:

Can anyone then supply in flight data that shows the aforementioned benefits?

I don't think anyone has set up flight data for this particular situation, maybe someone has or can do it for our enlightenment.  You should be able to reproduce the difference yourself if you fly and lean to roughness at WOT, then cock your throttle plate and see how much more you can lean with the throttle back a little bit.  Watch your EGTs.  Unless you have a very unusual setup, you will see a difference.  I always pull the throttle back until I see a movement in the Manifold Pressure and then move it forward until it returns to the original numbers.

Link to comment
Share on other sites

Just now, Jerry 5TJ said:

Just like “flying on the step” perhaps.

I haven't been trained on this one as much, but if I understand it correctly, It works.  I learned to do this in my Cherokee.  If I climb high, and pull power descending to my altitude I see a noticeable difference in cruise speeds.  Since noticing it, I've just always done that on the Mooney too.

Link to comment
Share on other sites

I asked the question for a reason- just because we all "do something" for a long time doesn't necessarily make it correct.

Without empirical data it's all just supposition and OWTs. 

Fuel distribution by moving the fly plate is not something noted in any Lycoming data that I have ever read. It may very well be there,  I just haven't seen it in my 50+ years reading this stuff. And, it might very well work but data is needed to verify. Not just, "we've done it this way for years".  Let's find someone willing to gather the data on 4 cylinder carb'd engines.

(Likewise, not many really understand the mechanical mixture enrichment system in our carb'd engines. It's not what many think. And, it plays no part once we lean the mixture for cruise. )

Most of the LOP and adding carb heat to improve distribution came from radial engines. P&W R-985s are ones that respond well to carb heat to improve cylinder to cylinder fuel flows but an intake temp gauge is needed to do it properly. 

Anyone with a 4 probe EGT can do it and write down the numbers. I have factory original 1 probe type stuff. 

"Flying on step"  Oh boy, here come the flaming arrows-

Transition to cruise flight from climb speed is all we are trying to do. How long that takes depends on several factors.

One can climb above cruise altitude and trade altitude for speed or one can leave climb power on, level at cruise altitude and let the speed accelerate to normal cruise before reducing to cruise power (this is this way I was taught in both DC-3s and 727s) in addition to Navajos, Citations and Cessna 150s. Both ways will get you to the proper ATTITUDE for cruise. 

If one levels at cruise altitude and immediately pulls back to cruise power then the time to accelerate to cruise speed will be drawn out and (depending on weight and altitude) you may never get there. Take a jet above its optimum cruise altitude for the weight and all it does is mush along. Same with us in our bug smashers. Don't get it up to speed first and it just mushes along at a higher angle of attack (due to low speed), at a higher drag regime (due to the high angle of attack and higher induced drag). If one wants to call flying in cruise condition at the optimum angle of attack being "on step" I no real problem with that moniker. 

Link to comment
Share on other sites

Cliffy- here's all I know:  

-at WOT, leaned a little bit, my #1 EGT gets really high, and #4 is usually the lowest.  2 and 3 are in between.

-pulling back the throttle so that the MP just barely moves (like a hair width) all the EGTs level out so my engine monitor looks like it was installed on a fuel injected engine.

-if I add just a touch of carb heat, and lean a little more, I can almost get all of my EGT bars flat.  No shit, like less than 20° difference from each other.

With results like that, over the course of about 15 years of M20C ownership with an engine monitor, I really don't care about empirical data because I can see it with my own two eyes.  And the engine smooths out, too, so I can literally feel the difference.

  • Like 2
  • Thanks 1
Link to comment
Share on other sites

I have a good engine monitor and spot on fuel flow data. I have been unable to replicate the widely  reported benefits of pulling the throttle back slightly in cruise, or of adding a little carb heat, upon mixture distribution. I would imagine any benefit from the latter comes at a specific carb temp.  To me benefit means being able to lean to lower fuel flows without roughness, which is subjective (or at least not captured on an engine monitor).  Of course I can’t prove a negative (i.e. it never helps), and I welcome objective evidence in favor of either practice.  

Link to comment
Share on other sites

I tried many times and was always unable to run smooothly at any measurable amount LOP regardless of what I did (varied throttle position, all kinds of different amounts of carb heat).

Then I started reworking my doghouse (over two annuals) and replaced my muffler that had a fist-sized hole in the bottom (barely visible while mounted). Now I can run smoothly 25° LOP. But not having an engine monitor yet, I don't cruise there.

Link to comment
Share on other sites

Speaking of OWT, a number of inmates here have reported in the past that empirically their Mooney’s burned through less oil if they did their ascents at 25 squared rather than 2700 and WOT.  It’s been my practice only because that’s what it says to do in my POH.  The Lucky Strike seems to have plenty of get up and go at that power setting.

 

Really good thread, comparing best practices.  This thread should be a sticky.

  • Like 1
Link to comment
Share on other sites

1 hour ago, steingar said:

Speaking of OWT, a number of inmates here have reported in the past that empirically their Mooney’s burned through less oil if they did their ascents at 25 squared rather than 2700 and WOT.  It’s been my practice only because that’s what it says to do in my POH.  The Lucky Strike seems to have plenty of get up and go at that power setting.

 

Really good thread, comparing best practices.  This thread should be a sticky.

+1 for 25x25 in the climb.  As soon as I am clear of the pattern, this is what i set up for.  On my trip to DC last weekend (3 hours total flying time), oil level was the same sunday after final landing as it had been friday before takeoff.

Link to comment
Share on other sites

When I got the Mooney and used 25 squared, the transition instructor put me onto everything forward for climb out at 105 IAS.  I saw that corraborated on this forum and have done so ever since.  I am all ears for reasons for each method.

Link to comment
Share on other sites

The 1968 POH on my C says to pull back to 26-squared once away from the ground, and that's what I did at first. Cooling certainly was a problem, so I would pitch from Vy (105mph) to 120mph above 500 AGL, which helped some. Then I read the modern consensus that pulling back the throttle actually hurts cooling by cutting out the carb enrichment circuit, so I kept everything forward for the whole climb* .  I noticed little difference in cooling with throttle full forward, but climb at 120 mph is a tad faster. Then I tried 25-squared. I noticed it is indeed cooler as I climb at 120mph, but then climb rate suffers, and I have to pitch to slower speeds at lower altitudes to maintain 500fpm, thus negating the cooling benefit.  So I settled into maintaining WOT, pitching to 120mph above 500 AGL, and pulling back RPM to 2600-2650 to cut engine noise once above 2000 AGL. Cooling is still an issue. I think the need for all this discussion comes back to the exceptionally unfavorable interaction among the crappy cowl design, the doghouse baffle, and the carb'd O-360 parallel valve Lycoming. All three together are needed to generate complete cooling misery in climb. I don't hear E and F model owners routinely bitching like me.  Or maybe it's just my personality :lol:.

 

*except leaning a bit at higher altitudes when power drops below 75% and I can keep CHTs <400, though making it all the way to "target EGT" and staying <400 CHT in climb is hopeless.

  • Like 1
Link to comment
Share on other sites

Several things come to mind...

1) if you have a FF gauge, and you don’t see a stepwise decrease in FF as you back the throttle out... something may be amiss with the carb linkages...  there is physically a second fuel jet that gets opened and closed in the last few mms of operation of the throttle control...

The extra jet is specifically there to increase FF for cooling the engine during high power T/O...

2) Controlling CHT is always a challenge.  It is often improved with higher IAS.  With a minimal cost to the indicated VS...  Many around here use 120 to climb towards their cruise altitude...  it provides a combination of better cooling and better groundspeed...

3) The two fuel Nozzles spray some pretty large droplets in a not so random pattern. An improved fuel distribution strategy can be used...

  • adding carb heat is a good way of adding energy to evaporate fuel molecules, separating more fuel from the droplets...
  • Adding turbulence (air swirling)to the air flow, acts as a mixer to the air/fuel stream, this spreading the droplets out and around some more.  Interesting discussion of transport phenomena and molecular distribution...turbuleant flow vs laminar flow... the throttle plate in the way of the airflow will add some turbulence....

4) Cutting back on MP also has a method of cutting back the amount of heat generated in the same amount of time.  In NA Mooneys, this happens pretty quickly on its own as MP drops with altitude and so does the FF...

5) An interesting thing that doesn’t seem to be discussed often enough... the target EGT method...Blue box...white box....  This is the method used for making sure that excess FF is set to maintain the additional cooling during the climb... the bluebox is an analog EGT arc on some Mooneys.  It is in the range of 200-300°F ROP...  older Mooneys didn’t get much discussion on this technique and didn’t get a blue box for climb mixture setting.

To separate these ideas from OWTs... actual data, from actual instruments, should supply the results...  the Blue box is covered in the ship’s POH.

 

Dev,

are you seeing a step in FF as the second fuel nozzle opens/closes?

 

For improved FF distribution... Add a fuel injection system...  unfortunately, that includes swapping out an entire engine and an STC from Lasar.  Not a bad option if you have settled on your M20C as your forever Mooney, and it’s engine is in line for an OH.  :)

 

PP thoughts only...

Best regards,

-a-

  • Like 1
Link to comment
Share on other sites

17 minutes ago, carusoam said:

A few things come to mind...

1) if you have a FF gauge, and you don’t see a stepwise decrease in FF as you back the throttle out... something may be amiss with the carb linkages...  there is physically a second fuel jet that gets opened and closed in the last few mms of operation of the throttle control...

The extra jet is specifically there to increase FF for cooling the engine during high power T/O...

2) Controlling CHT is always a challenge.  It is often improved with higher IAS.  With a minimal cost to the indicated VS...  Many around here use 120 to climb towards their cruise altitude...  it provides a combination of better cooling and better groundspeed...

3) The two fuel Nozzles spray some pretty large droplets in a not so random pattern. An improved fuel distribution strategy can be used...

  • adding carb heat is a good way of adding energy to evaporate fuel molecules, separating more fuel from the droplets...
  • Adding turbulence (air swirling)to the air flow, acts as a mixer to the air/fuel stream, this spreading the droplets out and around some more.  Interesting discussion of transport phenomena and molecular distribution...turbuleant flow vs laminar flow... the throttle plate in the way of the airflow will add some turbulence....

To separate these ideas from OWTs... actual data from actual instruments should supply the results...

Dev,

are you seeing a step in FF as the second fuel nozzle opens/closes?

Best regards,

-a-

Hard to say Anthony - it would be interesting to try pulling throttle very slowly at first to try to find the "step" after leveling for cruise. I'm gonna give it a shot sometime.  Do you know how much fuel flow the enrichment circuit adds at full power?  My my max FF is very close to the expected 18gph.

The touch of carb heat tweak for mixture distribution does not make sense to me, though I've tried it many times, with no obvious effect on EGTs.  It would seem that at a given MP, any added benefit of carb heat on initial fuel vaporization would be highly contingent on carb temp.  My carb temp gauge with carb heat off in cruise reads anywhere from the low teens to the high 40s F depending on atmospheric conditions. The effect of cracking the carb heat open to raise the temp a couple of degrees may vary widely based on the temp baseline. Has anyone studied the optimal carb temp for even mixture distribution in an O-360? It seems like a pretty simple experiment. I have not noticed  obvious differences in mixture distribution based on carb temp in cruise. Admittedly I have not looked carefully, although the data is there for hundreds of flights in my EDM-900 if someone's kid wants to make a high school science fair project of it ;)

My physics is weak - am I missing something basic??

Link to comment
Share on other sites

Hmmmm....

How does that Valve work? I don’t remember what kind of valve it is inside the carb.... It might open more over a range... probably not very linear either...

A graph of MP vs. FF would show an inflection point as the second nozzle starts flowing....

 

The important part is the max FF is set properly.  Probably not possible without the second nozzle being open....

 

Some additional PP thoughts... probably need a mathematician to finish all the calculations based on all the degrees of freedom...

  • The amount of fuel being drawn into the carb is based on the pressure difference between the Venturi and the fuel bowl...
  • FF is actually determined by the airflow going through the Venturi and nozzle sizes...
  • The Two fuel nozzles are not the same size, so a moderate step may be harder to notice.

The scale of the additional fuel flow is also a challenge to put a finger on...  18gph at WOT, SL, and full mixture, vs cruise MP setting with the mixture leaned 9gp... is unable to say what the FF for the extra circuit is...

One way to look at finding the answer could come from comparing The Long Body’s Blue box leaning method... in this case WOT, mixture in, fuel pump comes on automatically, this supplies the same 2X FF in T/O vs. cruise...  30 vs. 15 gph (roughly).  What this indicates is the EGT is actually lower outside the blue box indicating >300°F ROP...

To get a rough idea of the FF generated solely by the enrichment circuit...  in cruise, at a high MP setting, compare the FF near peak to the FF with the mixture pushed all the way in... you can back out the FF used for the other parts of the operation, leaving the enrichment part visible...

An example from the IO550.... cruising 100°F ROP 15gph,  LOP 12.5 gph (more rough numbers)

looks like 2.5 gph is being used for each 100°F ROP...

If I climb at 300°F ROP that would be more like 7.5gph used by the IO550 to provide additional cooling...

In the climb, I set the mixture at 200°f ROP, top of the blue box, as the altitude rises, the EGT falls out the bottom of the blue box, mixture gets readjusted...

How does this apply to the M20C....?

  • Looks like we are roughly using the same target EGT method.  My EGT gauge, just has a blue box.
  • Excess FF comes from somewhere to provide deep ROP EGTs for T/O and climb.
  • The M20C uses the mechanical enrichment cycle employing the second fuel nozzle.
  • The IO550 defines and displays the excess fuel used for cooling as the EGT being kept in the calibrated blue box...
  • My simple math indicates... 7.5gph keeps the peak EGT  lowered to the deep ROP zone.... 7.5 - 5.0gph...
  • The IO550 use 50% more fuel, generally, than the M20C...
  • So if the IO550 generally uses about 6gph for the extra cooling... 
  • The M20C probably uses about 4gph to stay in the target EGT zone..?
  • if a full sweep of the mixture in cruise uses 2gph, the extra 2gph would come from the enrichment circuit...

The more I think about this... the more I think I remember a number being given for the gph of the enrichment circuit... something in the range of 1-3gp?  

Would that number be in the carburetor manual, or in the Lycoming manual? There are a few different choices for the size of the second nozzle. Logs and part numbers will let you know what you have installed....

The usual... lots of PP thoughts, not many real answers.... :)

Best regards,

-a-

 

 

 

 

Link to comment
Share on other sites

On 3/16/2018 at 3:03 PM, cliffy said:

I asked the question for a reason- just because we all "do something" for a long time doesn't necessarily make it correct.

Without empirical data it's all just supposition and OWTs. 

Fuel distribution by moving the fly plate is not something noted in any Lycoming data that I have ever read. It may very well be there,  I just haven't seen it in my 50+ years reading this stuff. And, it might very well work but data is needed to verify. Not just, "we've done it this way for years".  Let's find someone willing to gather the data on 4 cylinder carb'd engines.

(Likewise, not many really understand the mechanical mixture enrichment system in our carb'd engines. It's not what many think. And, it plays no part once we lean the mixture for cruise. )

Most of the LOP and adding carb heat to improve distribution came from radial engines. P&W R-985s are ones that respond well to carb heat to improve cylinder to cylinder fuel flows but an intake temp gauge is needed to do it properly. 

Anyone with a 4 probe EGT can do it and write down the numbers. I have factory original 1 probe type stuff. 

 

I'm in full agreement regarding OWT's and doing something just because "we've always done it this way". 

I don't have the data any longer as I sold the airplane. But when I owned and flew N6XM, 400 hours over the course of two years, I did everything I could to try to get good LOP operations with the carby engine. I repeatedly ran a GAMI lean test to measure fuel distribution between cylinders. Obviously I didn't have GAMI injectors as the O360 is carbureted and doesn't have injectors. But the GAMI lean test is still valid for measuring fuel distribution. A spread of 0.5 gph between the first and last cylinders to peak is usually close enough for smooth LOP opps. I was never saw fuel distribution of less than 1 gph until I tried "cocking" the throttle. I would pull the throttle back just until the MP needle started to move. This method allowed me to see a "GAMI" spread of sometimes as low as .3 gph between the first and last cylinder. Those numbers allowed me to run quite far LOP. It didn't always work, but without the throttle adjustment, I was never able to get a narrow enough spread to run LOP smoothly.

I used an Insight G2 with fuel flow for this measurement.

One note is that I'd never do this below about 8000 ft. So I was already running relatively low power even at WOT. 
Another note is that I never experienced any benefit from carb heat in attempting better fuel distribution. 
Finally... along with much tighter fuel distribution, I got much better CHT's. This would be a natural result of having all cylinders in close to the same position on the EGT curve.

I realize this isn't the answer you asked for as I don't have the raw data. But for what it's worth, I did the measurements, collected and analyzed the data when I owned the plane that made it relevant. 

  • Like 2
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.